The present invention relates to optoelectronic devices which generate a light emission, and more particularly, to a highly conductive carrier tunneling current aperture for laser diodes and related optoelectronic devices.
Highly efficient laser diodes, especially those having a vertical resonator and producing transverse single mode emissions, require transverse current constriction to a diameter of 10 microns or less. The additional voltage drop due to the presence of the current aperture results in an increased threshold voltage. Channeling the injected current through such small areas also generates additional heat inside the device. The more heat that is generated, the lower maximum optical output power due to the thermal rollover of the light-current-curve. The heat generated inside the device is also responsible for the presence of a thermal induced lens which enhances the creation of undesirable high-order transverse modes. Variations of the radial distribution of the complex refractive index (both real and imaginary parts) induced by the aperture results in scattering losses.
Previously known techniques for current confinement in laser diodes are mesa etching or proton implantation. In vertical cavity surface emitting lasers (VCSELs) as well as edge-emitting devices, very high electro-optical conversion efficiencies are achieved by constricting the current via selectively oxidized apertures. In VCSELs formed from type III-V semiconductor material systems, like InAlGaAs, often the oxidation of the aluminum containing layers is used, as disclosed by U.S. Pat. No. 5,262,360. These high aluminum content layers are generally surrounded by layers of far less aluminum content. During oxidation, aluminum arsenide (AlAs) is transformed into AlxOy layers with thicknesses usually below 100 nm. Current flow through the aperture perpendicular to the individual planes of the layers is limited by electrical resistance of the aluminum containing layers inside the aperture, except in very thin layers where the limitation is almost exclusively a function of the heterojunctions between the layers having high and low aluminum content. Due to the step in the refractive index at the perimeter of the aperture, considerable scattering of the optical wave is induced, resulting in increased resonator losses. Shrinkage of the AlxOy layer also leads to strain in the semiconductor crystal, which has a negative effect on the stability and life of the device.
The present invention provides an optoelectronic device having a highly conductive carrier tunneling current aperture. The device includes a centrally positioned current aperture formed from a quantum layer made of a III-IV-V semiconductor compound, which is doped with a first doping type. The current aperture is laterally confined by an oxide of the III-IV-V semiconductor compound. Adjacent layers are also formed of a semiconductor material that is doped with the first doping type.
The use of the III-IV-V semiconductor compound provides the highest possible electrical conductivity in the current aperture opening, with minimal optical losses due to scattering and defraction of the oscillating mode. Additionally, internal stresses created during the formation of the aperture are minimized in the multilayer semiconductor structure due to the reduced change in size of the oxide of the III-IV-V semiconductor material in comparison to the previously used III-V semiconductor materials.